SPONGES 



2f 



marked are inhabitants of Bhallow water ; or, if not, they are 

 forms whose ncarcKt allifjs are to be found along the shore, and 

 whose ancestors have probaljly migrated into dcep«;r water in com- 

 |>arativ*;ly recent timers. In other words, the "impersonal" con- 

 dition, aa it may be termed, seems to have been correlat^^d at its 

 first origin witfi life in a habitat where the sponge has \Ai contend 

 with, and to adapt itself to, the action of stresses and strains which 

 are always very variable and often very severe, and where the 



HjiongUla Uiynutris, auct. (after 

 W<;ltri<;r). i- 



FlO. 34. 



Ch/dina ocubjJUi, Pall, half-natural «i»!. 

 ote, (Mcula ; it, atalk. 



form of the sponge becomes of the greatest importance in the 

 struggle for existence. Hence the sponge colony as a whole takes 

 on some characteristic mode of growth which may vary greatly 

 from species to species, or even in different specimens of the same 

 species. In this way a great numh»er of different shapes and forms 

 arise whicli are often extremely irregular and amorphous, but which 

 can usually be classed under one of a series of typical forms. 

 As the starting-point we may conveniently take a small com- 

 pact sponge with numerous oscula — that is to say, a colony in which 



